Shaped charge



Filed June 27, 1956 weep/N D. MEDD/CZ INVEN TOR.

3,627,833 SHAPED CHARGE Lot-rain D. Meddiclr, Whittier, aCalif, assignor, by mesue assignments, to Borg-Warner Corporation, Vernon Calitl, a corporation of iilinois Filed June 27, 1%&, Ser. No. 594,255 3 (Jlaims. (QR. 162-24) This invention relates to explosive devices and more particularly to an improved device of the shaped charge type by which a greater penetration can be achieved from a smaller quantity of explosive.

It has been found that highly superior results are ob tainable from a given shaped charge unit by interposing a suitable barrier member between the detonator and the apex of the liner for the unit. More specifically, exper1- ments have established that a unit of this type equipped with a barrier having a broad base and a short axis provides highly superior results from the explosive charge and avoids the necessity for the close manufacturing tolerances characteristic of the barrier member heretofore employed. While the manner in which the barrier cooperates with the other elements of its environment to produce the beneficial results observed by its use are not fully understood, analysis of the evidence obtained experimentally indicates that the barrier of this invention controls the detonation of the main charge in a manner providing a more efiicient and effective utilization of its available energy. For example, it appears desirable to provide means in the form of a properly designed barrier for dampening the shock wave of the primary detonation centrally of the charge sufficiently for the radially moving portion of the shock wave to approach the peripheral extremities of the charge proper and thereafter to complete the detonation from the peripheral area. Further beneficial effects are obtained if a secondary detonation of the charge is effected on the forward side of the barrier at a point such that the secondary shock wave merges with that of the primary detonation opposite the peripheral rim area of the barrier member. Under these conditions, it appears that the merging wave fronts combine additively to augment the force of the penetrating jet.

Accordingly, it is an object of this invention to provide a new shaped charge type explosive unit having greater penetrating power with a given quantity of explosive.

Another object of the invention is the provision of a shaped charge unit having a shock wave barrier member of unique design interposed between the detonator and the apex of the liner element.

A further object of the invention is the provision of a shaped charge having a barrier embedded in the explosive material so arranged that the detonation of a principal portion of the material proceeds from the peripheral area of its base rather than axially of the material.

Still another object of the invention is the provision of a shaped charge unit with a barrier member designed to effect a secondary detonation of the explosive material forwardly of the barrier by the force of the primary detonation shock waves transmitted through the relatively thin rim edge of the barrier.

These and other more specific objects of the invention will become apparent from the following detailed specification of an illustrative embodiment taken in connection with the accompanying drawing wherein:

FIGURE 1 is a longitudinal sectional view taken axially of a shaped charge unit incorporating the present invention;

FIGURE 2 is a transverse sectional view taken along the broken line 2-2 on FIGURE 1; and

3,h27,838 Patented Apr. 3, 1952 FIGURE 3 is a view in perspective of the barrier member forming an important feature of the invention.

Referring to the drawing, there is shown in FIGURE 1 a shaped charge unit designated generally 10 suitably di mensioned for use in a perforating gun of the type commonly employed in earth boreholes. In this application of a shaped charge unit, a plurality of the explosive devices are mounted in a tubing adapted to be lowered into a borehole, such as an oil well, following which the units are detonated to form oil flow cavities extending radially into the oil bearing strata. To be useful, the cavity-forming jet from the shaped charge unit must pierce a sealing cap for the unit, the well fluid filling the borehole, the well casing, the cement encircling the casing and thereafter the oil-bearing strata. Accordingly, it is important to utilize the available energy within the explosive agent at the highest possible elficiency to the end that a cavity of maximum length may be formed in the oil-producing strata. The unit illustrated has been found highly superior to prior constructions in achieving these objectives and comprises an exterior casing 11 hav ing a cylindrical body 12 open at its discharge end 13. The generally frusto-conical end wall 14 is formed with an axial well 15 seating a booster charge 16. Extending across the bottom of well 15 is a bore 17 for a suitable igniter for booster 16 such as a Primacord 18 retained by a split ring holder 19.

The explosive charge 2%) contained with the main body of casing 11 has a generally conical concavity axially of the casin formed by a thin-walled conical liner 21. The peripheral forward rim of liner 21 has a press fit with the interi r side wall of casing 11 and its apex 22 is aligned with the axis of the casing and spaced forwardly of the forward end of booster 16 as is made clear by FEGURE 1.

' It will be understood that liner 21 may be made of various materials including metals and non-metals; however, copper is a preferred material due to the ease with which it can be worked and the superior results obtained with this material. It will also be understood that the inclination of the liner side walls and the apex contour may be varied over a considerable range to obtain an optimum penetration with a given explosive material.

The penetrating power of the shaped charge unit is increased to a marked degree by interposing a conical mem' ber designated generally 25 between the booster 16 and apex 22 of liner 21. This barrier, preferably made of metal, has a broad base arranged at right angles to the axis of liner 21 and of casing 11. Its axial thickness, though not critical, should be suificient to dampen the shock wave of the detonating explosive material under lying the base of barrier 25 to an extent preventing detonation of the explosive surrounding the apex area of the barrier. For this reason best results are obtained by using barrier members of different axial thickness with explosive charges of different compositions. Owing to the conical shape of barrier 25, its thin and tapering rim edges are of insufficient thickness to dampen fully the high order detonation of the relatively thin layer of explosive material underlying the base of the barrier memher. In consequence, a low order secondary detonation of charge 26 is believed to take place in a closed ring on forward inclined surface of the barrier member with the beneficial results to be explained in greater detail below. While the explanation of the superior results obtained from shaped charge units incorporating the above-described conical barrier are not thoroughly understood, the following theory and conclusions have been evolved on the basis of observation and experimental results. Firing of the unit is accomplished in the usual manner by detonating the igniter core 18 which in turn detonates booster 16. The latter develops the high-powered shock wave required to detonate main charge 26 axially thereof and behind barrier member 25. The forwardly advancing high order shock wave representing the primary explosion proceeding through charge 20 appears to be dampened or absorbed in passing through the central portion of barrier 25 to such an extent as to prevent the direct detonation of that portion of charge 20 immediately forwardly of the barrier. However, dampening of the high order shock wave to a lesser degree occurs in the thinner rim areas of the barrier with the result that a secondary low order detonation occurs in an annulus on the forward side of the barrier and near its thin rim edge. It will therefore be understood that the area of initiation of the low order detonation is governed largely by the thickness of the barrier at its center and the angle of taper of its forward conical surface. The merger of the primary and secondary shock waves near the periphery of the barrier creates a very high pressure of the order of 10,000,000 p.s.i. which is effective to penetrate the apex of the conical liner and form a jet axially of the cone having tremendous velocity.

Although only a single embodiment of the barrier element 25 has been illustrated and described it will be understood that the barrier may be formed in various shapes and sizes so long as the essential principles described above are adhered to. These include a disk or cup-like element having a relatively thick central area effective to dampen the shock Waves of the burning explosive therebehind and having a thinner region adjacent its periphery through which a low order detonation can be initiated. Barriers embodying these features have been found self-regulating by reason of the wide variation in the thickness of the central and rim areas thereof and to be highly superior as respects their penetrating capabilities.

It is evident that in the light of the present disclosure modifications of the mode and apparatus herein disclosed as exemplary will occur to those skilled in the art, and accordingly it is not desired to be limited to the specific details of the illustrative mode and apparatus, but what is claimed is:

l. A shaped charge explosive unit comprising: a casing; a shaped charge of explosive material seated within said casing, said charge having an outwardly-flaring generally conical cavity formed in the front face thereof; liner means lining the walls of said cavity; detonator means for igniting said shaped charge in a zone rearwardly spaced from the apex of said cavity and positioned axially thereof; and a disk-shaped solid body of metal interposed between said detonator means and the apex of said cavity, said body being positioned coaxially of the axis of said cavity and being spaced from said detonator means and from the apex of said cavity, said body being completely surrounded by said explosive material with the entire exterior of said body in contact with said explosive material, said body having a thick central section and a thin circular rim, said body tapering gradually and substantially uniformly from its axis to its rim, said central section of said body being of such thickness as to dampen the primary high order shock wave originating in the explosive material rearwardly of the body to an extent to prevent direct detonation of that portion of the explosive material immediately forwardly of said central section, said body having an annular section intermediate said central section and said rim of such thickness as to dampen said high order shock wave to a lesser degree sufficient to initiate an annular secondary low order detonation in said explosive material on the forward side of said annular section, said secondary detonation merging with said primary shock wave near the rim of said body to create a detonation zone wherein the transient pressure is very great.

2. A shaped charge explosive unit comprising: a casing; a shaped charge of explosive material seated within said tsing, said charge having an outwardly-flaring generally conical cavity formed in the front face thereof; liner means lining the walls of said cavity; detonator means for igniting said shaped charge in a zone rearwardly spaced from the apex of said cavity and positioned axially thereof; and a disk-shaped solid body of metal interposed between said detonator means and the apex of said cavity, said body being positioned coaxially of the axis of said cavity and being spaced from said detonator means and from the apex of said cavity, said body being completely surrounded by said explosive material with the entire exterior of said body in contact with said explosive material, said body having a plane base and an opposed conical surface having a wide obtuse apex angle, the sides of said conical surface intersecting said base to provide said body with a thick central section and a thin circular rim, said body tapering gradually and uniformly from its axis to its rim; said central section of said body being of such thickness as to dampen the primary high order shock Wave originating in the explosive material rearwardly of the body to an extent to prevent direct detonation of that portion of the explosive material immediately forwardly of said central section, said body having an annular section intermediate said central section and said rim of such thickness as to dampen said high order shock wave to a lesser degree suficient to initiate an annular secondary low order detonation in said explosive material on the forward side of said annular section, said secondary detonation merging with said primary shock wave near the rim of said body to create a detonation zone wherein the transient pressure is very great.

3. A shaped charge explosive unit comprising: a cas ing; a shaped charge of explosive material seated within said casing, said charge having an outwardly-flaring generally conical cavity formed in the front face thereof; liner means lining the walls of said cavity; detonator means for igniting said shaped charge in a zone rearwardly spaced from the apex of said cavity and positioned axially thereof; and a disk-shaped solid body of metal interposed between said detonator means and the apex of said cavity, said body being positioned coaxially of the axis of said cavity and being spaced from said detonator means and from the apex of said cavity, said body being completely surrounded by said explosive material with the entire exterior of said body in contact with said explosive material, said body having a rearwardly facing plane base and a forwardly facing conical surface having a wide obtuse apex angle, the sides of said conical surface intersecting said base to provide said body with a thick central section and a thin circular rim, said body tapering gradually and uniformly from its axis to its rim, said central section of said body being of such thickness as to dampen the primary high order shock wave originating in the explosive material rearwardly of the body to an extent to prevent direct detonation of that portion of the explosive material immediately forwardly of said central section, said body having an annular section intermediate said central section and said rim of such thickness as to dampen said high order shock wave to a lesser degree sufficient to initiate an annular secondary low order detonation in said explosive material on the forward side of said annular section, said secondary detonation merging with said primary shock wave near the rim of said body to create a detonation zone wherein the transient pressure is very great.

References Cited in the file of this patent UNITED STATES PATENTS .Great Britain Sept. 1, 1954 

